installing a pump shut off switch, concrete question

[finse]

Over the weekend, I had a pretty big issue and a good 40% of my pond went to the grass. I've isolated the issue, and now I am working on preventing it from happening again. I have gotten a little giant cut off switch. I'd like to mount this on a pvc pipe placed in a planter full of concrete. However, I am worried that the concrete could cause issues with water quality, or even harm my fish.

Can anyone give me some advise on how to get this done right the first time?

 

[Waterbug]

I wouldn't worry about the concrete harming fish. Concrete myth.

 

[finse]

Thanks Waterbug!!

 

[crsublette]

Finse, if you are looking for more information, I found A long lesson on concrete one of the most informative threads. My recommendation and explanation is paraphrased from this hyperlink.

"The surface area contact between water and concrete is the variable that causes calcium carbonate to leach into the water. Porous concrete allows a higher water contact. Be sure to use a concrete that becomes very dense. A small container filled with concrete has only a small surface area when compared to all the water in the pond. In your situation, any pH increase will be negligible and possibly not even be detectable with a pH tester."

 

[finse]

Just for the hell of it, I decided this would be an interesting time to test a couple of things... I went ahead and mixed up some hydrolic cement from home depot last night. I had a 5 gallon bucket filled with tap water, I washed off my mixer in it, and then allowed my little project to set up in the bucket. There was a lot of stuff floating, and the PH was 9. (Really no surprise there, lots of lime in hydrolic cement, and like 3 gallons of water).

This morning, I refilled the bucket with new water, the initial PH test was right at 7. I'll do another when I get home and post my results. My guess, it will be right around 7.

Cheers!

 

[crsublette]

I doubt you will register much change. From what I understand, the ratio of total water volume capacity (i.e., pond's total gallonage) vs actual water contact with concrete surface area is what determines any pH contribution.

Yeah, found the picture below from Myths and Realities, Concrete Wash Water. However, this is assuming the water gets a full thorough contact.

 

[Waterbug]

I'm surprised water in a bucket of brand new concrete was only 9. I would have expected 14, so I was even surprised by the link Charles posted with a starting pH of about 12. Thanks to you both for the info.

In uncured concrete, in a small bucket, at 7 pH I assume the pH would rise to 8 or 9 given, I don't know, a week or two. But now, given the info you all provided, I wouldn't be betting cash.

What a difference this is. 10-15 years ago the mere mention of concrete in a water garden forum will have filled the thread with dozens of "experts" making wild claims of how dangerous cement is even near a pond and putting it in the pond would be so inhumane to fish that you should be arrested. I never thought attitudes would ever change so I happily surprised to not see that here. And someone actually doing a pH experiment...I'm tearing up a little.

One myth down..163 to go.

 

[richyd]

I wouldn't worry about the concrete harming fish. Concrete myth.

Interesting read.
My pond started off as a neutral PH. as I used concrete to build the waterfall the PH has increased to just over 8, But has now stabilized

 

[Waterbug]

Interesting read.
My pond started off as a neutral PH. as I used concrete to build the waterfall the PH has increased to just over 8, But has now stabilized

What's the KH and GH of your source water?

 

[finse]

Waterbug, I'll have to look at KH and GH when I get home. Regarding PH; The PH may have been much higher then 9, but my test kit only goes to 9. Yesterday, when I got home, the bucket was at/above 9 again. Rinsed and repeated, this morning it was at/above 9 again. As of this morning, it's been 36 hours, so there is still a chance it's curing. More updates to come.

 

[Waterbug]

The curing process has basically 2 parts. Primarily crystalline like structure forms around tiny bits of hydroxide (the high pH stuff) sealing it off. This process never stops, but 28 days is generally considered the cure time for concrete. At that point it is difficult for water to get at the hydroxide.

The second curing process is where CO2 reacts with the surface hydroxide to form calcium carbonate. Called carbonation which seals the concrete further. Calcium carbonate will raise pH to 7 - 7.8 when in water that's below 7.

My guess is your 9 pH is really 12 since your test is maxed out. You could wait the 28 days for it to cure and then repeat the test.

 

[finse]

yesterday evening, the bucket water's PH was at 8. I placed the apparatus in my pond last night, and the PH of the pond has not changed at all in the last 12 hours.